The present invention relates to pumping devices, and more particularly to syringes.
Syringes are in common use today by physicians, nurses, and other hospital personnel for a variety of purposes. Frequently, syringes have been utilized to pump fluid into a body cavity of a patient or a cavity in a therapeutic device under circumstances where the pressure attained in the cavity should be limited to a predetermined value. For example, during a spinal anesthesia procedure an anesthetic solution is pumped from a syringe through a needle into the sub dural space which is essentially an inelastic pouch, and thus only a specified maximum amount of the solution should be pumped into the space as determined by the pressure in the space. Similarly, various types of cardiovascular catheters are often threaded into blood vessels, after which a balloon adjacent the distal end of the catheter is inflated through use of a syringe. If the balloon is overinflated, particularly when the catheter is placed in a smaller vessel, the vessel may be ruptured. Numerous other catheters, such as endotracheal tubes and Foley catheters, are frequently provided with retention balloons which should not be overinflated, particularly when the balloon is obstructed by a body passage.
Few of the hospital personnel realize the considerable pressures which can be generated by a hand-operated syringe. For example, a 10 c.c. syringe may readily generate pressures in the range of 50-60 lbs./sq. in., the smaller syringes being capable of developing greater pressures for the same amount of force applied to the syringe plunger. It is thus apparent that considerable care must be exercised by the user when a syringe is utilized to pump fluid into a cavity space where only a limited amount of pressure is desired. In the past, tactile sense has been used when forcing the plunger into the syringe to determine when the maximum pressure has been attained by resistance to plunger movement. Such a procedure produces speculative results, at best, in preventing harm to the patient, particularly since the syringe may readily generate relatively high pressures.